ThreadLocal 解决simpledateformat线程不安全

SimpleDateFormat在多线程情况下会出现线程不安全的情况，故用ThreadLoacl 处理
/**
 * 用ThreadLocal处理simplDateFormat线程不安全
 */
public class DateUtil {

    public static SimpleDateFormat renderSimpleDateFormat(String pattern) {
        ThreadLocal<SimpleDateFormat> threadLocal = new ThreadLocal<SimpleDateFormat>() {
            @Override
            protected SimpleDateFormat initialValue() {
                return new SimpleDateFormat(pattern);
            }
        };
        return threadLocal.get();
    }

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(10);
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    String str = DateUtil.renderSimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
                    System.out.println(str);
                    countDownLatch.countDown();
                }
            }).start();
        }
        //TODO： await 不是 wait
        countDownLatch.await();
        long end = System.currentTimeMillis();
        System.out.println(end - start);
    }
}